The present invention relates to the field of hydrostatic units such as transmissions, pumps and motors. More particularly, this invention relates to closed cavity or reduced oil volume pistons that slidably reciprocate in the cylinder bores of hydrostatic units.
Conventional closed cavity pistons have been utilized in hydrostatic units for a variety of agricultural, turf care and construction equipment. A conventional closed cavity or reduced oil volume piston has an elongated cylindrical main body and a truncated cylindrical cap. One end of the main body is closed and the other end has a deep annular cavity formed therein. The cap has opposite closed and open ends. The open end includes an annular groove such that the cap registers and mates with the stem and outer wall of the main body at its open end. Then the cap and main body are conventionally welded together along a single transverse plane where their respective open ends meet. The result is a lightweight hollow closed cavity piston, but the cost and complexity of the machining operation make it a relatively expensive piston.
It is therefore a principal object of this invention to provide a method of simultaneously securing together by projection welding a cap and piston body having longitudinally spaced contact surfaces.
These and other objects will be apparent to those skilled in the art.
A method of securing a cap on a piston body includes forming a first annular V-shaped surface at an open end of a cylindrical piston body; forming a second annular V-shaped surface on an annular surface of an oil conduit in the interior center of the piston body; forming a cap to close the open end of the piston body and forming a pair of annular flat surfaces therein which are in contact with the first and second annular flat shaped surfaces on the piston body; placing the cap over the open end of the piston body and thereby placing the annular surface on the cap and the body in close intimate mating relation; and welding the respective mating annular surface of the cap and the piston body together by subjecting the cap and body to an extreme high current density to force respective mating annular surfaces together.